This invention relates, in general, to surface impedance and sheet resistivity circuits, and more specifically, to repeatable sheet resistivity circuits.
Tapered resistivity surfaces can be termed resistive cards. Resistive cards terminate metal edges to prevent scattering due to diffraction by forming impedance transitions from ground planes to antenna apertures or to free space. Uses of such resistive cards are the reduction of RF side lobes when placed on the ends of antennas, and reduction of scattering from edges of ground planes when located at an antenna's ground plane.
Current methods of producing resistive cards include depositing thin layers of conductive material on a substrate where the resistivity is controlled by the thickness of the layer. One method involves sputtering nickel alloy material onto the substrate. Sputtering, however, is very difficult to control and the distribution of the metal is variable across the resistive card. Other methods of generating resistive cards are similarly limited in controllability and distribution, and the resistivity values after fabrication are hard to determine.